Mechanical refrigeration systems, and related heat transfer devices, such as heat pumps and air conditioners are well known in the art for industrial, commercial and domestic uses. Chlorofluorocarbons (CFCs) were developed in the 1930s as refrigerants for such systems. However, since the 1980s, the effect of CFCs on the stratospheric ozone layer has become the focus of much attention. In 1987, a number of governments signed the Montreal Protocol to protect the global environment, setting forth a timetable for phasing out the CFC products. CFCs were replaced with more environmentally acceptable materials that contain hydrogen, namely the hydrochlorofluorocarbons (HCFCs).
One of the most commonly used hydrochlorofluorocarbon refrigerants was chlorodifluoromethane (HCFC-22). However, subsequent amendments to the Montreal protocol accelerated the phase out of the CFCs and also scheduled the phase-out of HCFCs, including HCFC-22.
In response to the requirement for a non-flammable, non-toxic alternative to the CFCs and HCFCs, industry has developed a number of hydrofluorocarbons (HFCs) which have zero ozone depletion potential. R-410A (a 50:50 w/w blend of difluoromethane (HFC-32) and pentafluoroethane (HFC-125)) was adopted as the industry replacement for HCFC-22 in air conditioning and chiller applications as it does not contribute to ozone depletion. However, R-410A is not a drop-in replacement for R-22. Thus, the replacement of R-22 with R-410A required the redesign of major components within heat exchange systems, including the replacement and redesign of the compressor to accommodate the higher operating pressure and volumetric capacity of R-410A, when compared with R-22.
While R-410A has a more acceptable Ozone Depleting Potential (ODP) than R-22, the continued use of R-410A is problematic, due to it's high Global Warming Potential of 2088. There is therefore a need in the art for the replacement of R-410A with a more environmentally acceptable alternative.
It is understood in the art that it is highly desirable for a replacement heat transfer fluid to possess a difficult to achieve mosaic of properties including excellent heat transfer properties and in particular heat transfer properties that are well matched to the needs of the particular application, chemical stability, low or no toxicity, non-flammability, lubricant miscibility and/or lubricant compatibility amongst others. In addition, any replacement for R-410A would ideally be a good match for the operating conditions of R-410A in order to avoid modification or redesign of the system. The development of a heat transfer fluid meeting all of these requirements, many of which are unpredictable is a significant challenge.
With regard to efficiency in use, it is important to note that a loss of refrigerant thermodynamic performance or energy efficiency may result in an increase in fossil fuel usage as a result of the increased demand for electrical energy. The use of such a refrigerant will therefore have a negative secondary environmental impact.
Flammability is considered to be an important, and in some cases, a critical property for many heat transfer applications. Thus, it is frequently beneficial to use compounds in such compositions to achieve, if possible a refrigerant, which is non-flammable. As used herein, the term “non-flammable” refers to compositions which are determined to be non-flammable in accordance with ASTM standard E-681-2001 at conditions described in ASHRAE Standard 34-2013 and described in Appendix B1 to ASHRAE Standard 34-2013.
It is critical for maintenance of system efficiency, and proper and reliable functioning of the compressor, that lubricant circulating in a vapour compression heat transfer system is returned to the compressor to perform its intended lubricating function. Otherwise, lubricant might accumulate and become lodged in the coils and piping of the system, including in the heat transfer components. Furthermore, when lubricant accumulates on the inner surfaces of the evaporator, it lowers the heat exchange efficiency of the evaporator, and thereby reduces the efficiency of the system.
R-410A is currently used with polyol ester (POE) lubricating oil in air conditioning applications, as R-410A is miscible with POE at temperatures experienced during use of such systems. However, R-410A is immiscible with POE at temperatures typically experienced during operation of low temperature refrigeration systems, and heat pump systems. Therefore, unless steps are taken to mitigate against this immiscibility, POE and R-410A cannot be used in low temperature refrigeration or heat pump systems.
It is therefore desirable to be able to provide compositions which are capable of being used as a replacement for R-410A in air conditioning applications. It is an additional benefit to be able to use the compositions of the invention in for example heat pump and low temperature refrigeration systems, wherein said compositions do not suffer the drawback of immiscibility with POE at temperatures experienced during operation of these systems.